The present invention relates to an ignition system for internal combustion engines. The ignition system includes a coil rod and a shaft in a cylinder head of the internal combustion engine, into which shaft the coil rod is inserted over a portion of its longitudinal extension.
German Patent No. 41 32 851 describes a coil rod that can be inserted into the shaft of a cylinder head of an internal combustion engine in a customary, not further represented manner.
The coil rod has a housing whose basic form is cylindrical. In the housing, a bar-shaped core is situated in a central position as the internal part of an open magnetic circuit. A primary winding and a secondary winding are disposed in a concentric manner around the core, each on a separate coil form. A tubular outer iron core in the form of a longitudinally slit return plate is situated around the secondary winding.
The exterior, peripheral surface of the return plate made of ferromagnetic material abuts on the inner surface of the plastic housing. Due to the extremely different thermal expansion properties between the ferromagnetic material and the plastic, a sturdy bearing arrangement of the return plate on the housing requires in an undesirable manner a high production expenditure, thereby rendering it more expensive to produce the ignition system.
In comparison with the related art, the ignition system for internal combustion engines according to the present invention has the advantage that the previously mentioned shortcomings are avoided. As such, the ignition system is designed in such a manner that the return plate of the open magnetic circuit is no longer attached within the coil rod, but supported in the shaft of the internal combustion engine, set apart from the coil rod.
As a result, on the one hand, the coil rod can be manufactured in a manner that is favorable from a standpoint of production engineering, without the critical connection of the housing to the return plate.
On the other hand, the bearing arrangement of the return plate in the shaft of the metallic cylinder head is unproblematic, since, in this instance, only minimal, non-critical differences in the thermal expansion properties occur between the two metals.
In addition, the return plate being highly prestressed in a self-holding manner can be inserted into the shaft, since the solid cylinder head can also absorb large compressive forces without the danger of gradually yielding to form cracks.
As such, also in this instance, a path favorable from a standpoint of production engineering is followed, thereby resulting in low production costs for the ignition system.